The present invention relates to a picture-in-picture (hereinafter referred to as PIP) television set and a video tape recorder, and more particularly, to a image processing circuit capable of producing multiple pictures simultaneously on a common display screen.
Generally, in a PIP display, a B-channel picture (hereinafter referred to as sub-picture), being inserted at a predetermined area of an A-channel picture (hereinafter referred to as main picture), is displayed at a size corresponding to that of one-ninth of main picture. Such image processing techniques, which display main picture and sub-picture from different image sources respectively on one display screen, are applied to television and VTR systems.
Each VT and TVR maker applies specific format for a PIP system, and the PIP processing systems have different properties from one another in accordance with each specific format. For example, some processing systems use a method which samples both the main picture signal and the sub-picture signal simultaneously to convert those to digital data, while the other processing systems use a method which converts only the sub-picture to digital data. Additionally, there is disclosed the method of displaying within the main picture a small picture having a different picture source from the main picture. However, by the remarkable progress of PIP technique, a technique which displays simultaneously the multiple different pictures has been disclosed. In addition, there is disclosed another prior art which displays two sub-pictures simultaneously in a main picture, whereby one of the two pictures is a still picture while the other is a moving picture.
In the beginning techniques for displaying the multiple pictures disclosed recently, the PIP system includes four sets of a PIP controller, a line memory and a field memory respectively, and displays the picture on the screen by a write control signal of the controller during the reading process of the image signal.
This method is already a widely-known technique, which samples sequentially B-Y, R-Y and Y signals. In this processing method, since the line memory and the field memory are constituted separately, the control methods thereof are also independent of each other. Accordingly, the image data can be written and read respectively. Therefore, in the above-mentioned conventional method, since each of the line memory and the field memory is controlled independently each of other, the control timing signals must be produced effectively to control the memories. In attaining the goal, there has been a problem in which the construction of the circuit becomes complicated and raises the production cost of the system employing this known method.